1. Technical Field
The present invention relates to a friction material for use as a disk pad, brake lining, clutch facing, or the like, especially as a disk pad, in applications such as motor vehicles, various industrial machines.
2. Background Art
Friction materials are produced by molding and curing friction material compositions that have a fibrous base, binder, and filler as main ingredients. Raw materials for these friction material compositions include, as a part thereof, raw materials that promote rusting (i.e., corrosion-promoting substances) such as raw materials having a low pH (acidic materials) and raw materials containing chlorine ions, sulfate ions, or the like, to secure the performance required of friction materials, such as wear resistance and a high coefficient of friction.
However, in the case of a disk pad, for example, use of such related art raw materials rusts the part of the rotor that contacts the disk pad during stoppage. The partial rust generated on the rotor leads to selective wear in this part with repetitions of braking, resulting in a thickness variation in the rotor rotation direction. Brake vibration thus occurs and causes noise generation.
A technique for removing such corrosion-promoting substances from a friction material is described in JP-A-58-121325, which discloses a related art friction material for use as a clutch face produced through the neutralization and removal via water washing with chlorine ions, sulfate ions, formic acid, and the like, and further, via a rust-preventive treatment that contains an abrasion-resistant powder having a pH of from 6.0 to 10.0. Similar techniques are described in JP-A-59-40018 and JP-A-59-170541. Furthermore, JP-A-61-276827 describes a related art friction material obtained by a method in which silver nitrate, lead nitrate, or the like is reacted with corrosion-promoting substances to fix the corrosion-promoting substances as insoluble substances.
However, the techniques described in JP-A-58-121325, JP-A-59-40018 and JP-A-59-170541 necessitate a prolonged treatment and prolonged removal because the related art friction materials have a microporous structure consisting of a fibrous base, binder, and filler as main ingredients. Furthermore, the technique described in JP-A-61-276827 necessitates a new apparatus and has problems concerning treatment and water washing because the friction material itself is treated.